Blender 2.83.4 Eevee viewport color and rendered color are different with transparency
display viewport render is OK


If I disable the transparency from the render properties panel under film I get what I'm looking for.

The viewer for the render image is broken and has been broken for a long time.It cannot display luminous pixels that are transparent at the same time.
PNG is a format that can't do that either. It cannot do associated alpha channel correctly.
If you look at the rendered image as color (not color+A)

Or add a black backround and use alpha over to composite you the image over it and you should see if the render is correct.
As for saving the image, save as EXR and everything should be fine.
More info:
Rendering fire animations with transparent background
Render semi-transparent volume with cycles
and
How do I get the Glare node to output transparent instead of Black background